A telecommunications system may comprise a radio network. A radio telecommunication network typically operates in accordance with a given standard (or several standards) which sets out what the elements of the network are permitted to do and how that should be achieved. A typical radio telecommunications network consists of a number of cells, and is thus often referred to as a cellular radio network. A cell is typically formed by a certain area covered by one or several base transceiver stations (BTS) serving mobile stations (MS; sometimes also referred to as user equipment UE) within the cell via a radio interface. Each base-station has a radio transceiver capable of transmitting radio signals in downlink to the mobile stations within the cell area and receiving radio signals in uplink from the cell area next to the base-station. By means of these signals, the base station can communicate with the mobile station (MS) in that cell, which itself includes a radio transceiver.
Each base station may be connected to a base station controller (BSC) or to any other controller functionality provided by the cellular network. Thus a mobile station (MS) within a cell of the system is continuously controlled by a node providing controller function. Examples of the network controller include said base station controller (BSC), a radio network controller (RNC) and a mobile switching center (MSC), but other control nodes may also be used for the implementation of the network control functionality. The controller can be linked further to the public telephone network and/or to other networks such as packet data networks. By means of this system a user of the MS can establish a connection to the public network via one or several base stations.
The location of the mobile station MS could be fixed (for example if it is providing radio communications for a fixed site) or the MS could be moveable (for example if it is a hand portable transceiver or “mobile phone”). When the mobile station is moveable it may move between cells of the cellular radio system. As it moves from one cell (the “old cell”) to another cell (the “new cell”) there is a need to hand it over from communication with the BS of the old cell to the BS of the new cell without dropping the call.
In addition to circuit switched services, radio communication systems may also provide packet data services for the users thereof. The packet data service is typically a connectionless service where information symbols are transmitted within data packets. The size and length of the data packets may vary. The information symbols are typically carried by means of packet data bearers. The transmission speed of a bearer is defined by a parameter referred to as bitrate. More particularly, bitrate defines the bit rate that has been allocated for a user of the packet data services. For example, in the WCDMA (Wideband Code Division Multiple Access) based systems bitrate values such as 16, 32, 64, 128, 256 and 384 kbits may be used.
Packet data traffic may include various kinds of data transmission, such as short messages or text only emails and transmission of large documents in the background and interactive browsing of the world wide web (WWW). To give an example about packet data traffic, an ETSI (European Telecommunications Standards Institute) packet data model is shortly described here. A packet service session may contain one or several packet calls depending on the application. The packet data call may also be based on a non-real time (NRT) packet data service. During a packet call several packets may be generated, which means that the packet call constitutes typically a bursty sequence of packets. To give an example, in a web browsing session a packet call corresponds to the downloading of a document. After the document is entirely received by the user terminal, the user may consume some time for studying the information he has just received before he takes some further actions, such as request more data. Thus the traffic may be very bursty and the amount of traffic may be difficult to predict.
The non-real time (NRT) packet services via an air interface are different from real time (RT) services (i.e. circuit switched services) via an air interface. Firstly, as mentioned, the packet data is bursty. The required bit rate can change rapidly from zero to hundreds of kilobits per second. Packet data tolerates longer delay times than real time services. Therefore the packet data traffic may be more readily controlled from the radio access network point of view. Fore example, in interactive services the user must get resources within a reasonable time, but in a background type services the data can be transmitted when the free radio interface capacity can be allocated for the transmission. Data packets can also be retransmitted by a radio link control (RLC) layer. This allows the usage of a worse radio link quality and much higher frame-error-ratio than what could be used for real-time services.
In addition to non-real time services, it is also possible to transmit real time services, for example service classes such as telephone conversations and streaming data transmission, over packet networks. An example of the real time packet data traffic is transmission of voice over IP (Internet Protocol), i.e. so called Internet calls.
Packet scheduling function is employed to fill the any ‘empty’ capacity the packet data bearers may have. The empty capacity means potential capacity not currently used e.g. by circuit switched data, speech or signalling traffic. In other words, the packet scheduling tries to find any potential remaining network capacity for the packet data. More particularly, the function of the packet scheduling is to allocate, modify and release bitrates for the packet data service users in a dedicated transport channels (DCH) based on specific predefined parameters.
The scheduling may, however, not always be a straightforward operation to accomplish, for example because the load in the network changes dynamically. Also, packet data bearers in the DCH may have different bitrates and duration. The length of calls may also vary significantly and unpredictably, i.e. the cell load may be very bursty. If there are too few DCH allocations for the packet data bearers at the same time or if the allocated bit rates are too slow the available capacity may not be well and/or efficiently used. On the other hand, if there are too many DCH allocations for the packet data bearers or if the allocated bitrates are packet data bearers that have relatively high bitrates, the network may become overloaded.
A bitrate has to be allocated every time a new radio link is established between a mobile station and a base station. Because a controller, such as the radio network controller RNC, may handle a substantial number of radio links, a bitrate allocation may occur fairly often. This requires a substantial capacity from the controller. Once a bitrate has been allocated for a bearer, the bearer will have the allocated bitrate for either a limited or unlimited period of time, depending the application. However, the load conditions may change. This change may also be rapid and/or unpredictable. In addition, as there may exist several packet data bearers at the same time, the priority order between these may change. Therefore, what is needed is a flexible and preferably a dynamic solution for packet data scheduling.